Plant-based diets are associated with better health outcomes especially with regard to cardiovascular health with the benefits often attributed to the exceptional nutrition profile and overall lower energy density of plant foods.

With the growing consumer trend for plant foods and plant-based eating, the question has been raised with regard to the quality of plant-based diets and whether all plant-based dietary patterns are associated with improved health outcomes.

The ATTICA study¹ recruited adult males and females from around the Athens region in Greece between 2001 and 2002 to assess cardiovascular disease (CVD) outcomes based on various risk factors including blood lipids and anti-inflammatory markers, lifestyle and diet, socioeconomic and psychological factors.

Dietary assessment was based on food frequency questionnaires and calculation of the adherence to the Mediterranean diet.  A plant-based diet indices (PDI) score of 0-55 was allocated to diets, the higher the score the higher adherence to the mainly plant-based dietary recommendations of the Mediterranean diet.  The team also developed scores to further categorise between healthy (hPDI) and unhealthy (uPDI) dietary patterns.  The former having a greater intake of wholegrains, nuts, unsaturated fat, nuts, legumes and fruit and vegetables whilst uPDI score would indicate higher intakes of refined carbohydrates, salt and saturated fats.

Just over 2,000 participants (n=2,020) provided data at the 10-year follow up (average 8.4 years) between 2011 and 2012 and there were 317 cases of CVD events.

Overall PDI score (adherence to the Mediterranean diet food groups), demonstrated an inverse association with CVD outcomes.  Those in the third tertile for PDI scores had an overall 46% reduced CVD incidence compared to those in the first tertile.  However, there was a large variance for the HR from 0.14-2.25 which makes the findings inconclusive.

The evidence was much stronger when the team compared CVD outcomes with the hPDI and uPDI scores.

The uPDI scores showed a clear dose-dependent positive association with CVD outcomes.

• A 34% increased CVD risk for every 5 units increase in the uPDI score  (HR 1.34; 95% CI, 0.95-2.37)

Conversely those with a hPDI scores showed an inverse association with CVD outcomes.

• Those in the third tertile for hPDI score showing a 68% reduced CVD incidence compared to the first hPDI tertile (HR 0.32, 95% CI, 0.16-0.63, p=0.003)
• Even those in the 2nd tertile for hPDI scores had a 47% reduced CVD risk compared to the first tertile (p=0.003).

This study confirms the earlier and much larger 2017 study by Satija and colleagues.²  The team compared the plant-based diet index (PDI) scores of food frequency questionnaires from over 4.8 million US adults participating in large cohort studies. Just like the ATTICA study, the group produced an overall PDI score as well as further categorising diets according their hPDI and an uPDI scores. Scores were compared to coronary heart disease (CHD) indices.

The research team’s findings were similar to the current ATTICA study. They demonstrated an inverse CHD risk with higher overall PDI scores, a positive association with uPDI scores and an inverse association with hPDI scores.  The study found a 32% increase CHD risk for those following a diet with uPDI score (HR 1.32; 95% CI, 0.68-0.83, p <0.001).  Conversely, diets classified as hPDI demonstrated a 25% reduced CHD risk (HR 0.75; 95% CI, 1.20-1.46, p <0.001).

With the urgency to shift population groups to more plant-based eating habits, it is critical that the communication is clear with regard to which plant foods the population should be moving towards such as whole grains, fruit and vegetables, nuts and legumes including soya.